The microscopic populations of bacteria in our intestines are, in some ways, just like us: They live in communities, eat, work, reproduce, and eventually die. Some live in harmony with our bodies but others don’t, putting us at increased risk for a variety of diseases. Now, Caltech researchers in the laboratory of Sarkis Mazmanian, Luis B. and Nelly Soux Professor of Microbiology, Heritage Medical Research Institute Investigator and TCCI®-affiliated faculty member have discovered that a certain species of bacteria behaves differently depending on where in the gut it takes up residence.